MC68HC05L16 Datasheet, PDF (24/146 Pages) Freescale Semiconductor, Inc – Microcontrollers

Memory Map
2.2 Input/Output and Control Registers
The input/output (I/O) and control registers reside in locations $0000–$003F. A summary of these
registers is shown in Figure 2-3. The bit assignments for each register are shown in Figure 2-4. Reading
from unimplemented bits (denoted by shading) will return unknown states (unless explicitly defined to
read 0), and writing to unimplemented bits will have no effect. See also Figure 2-2.
Register Address (Main map unless otherwise specified)
Register Name (Full)
Read _{Read-Only Bit}
Bit Name (Mnemonic)
$003E
Read: FTUP STUP
0
Miscellaneous Register _Write:
(MISC)
Reset: *
*
0
Write
Reset Value
Register Name (Mnemonic)
0
SYS1 SYS0 FOSCE OPTM
0
1
0
1
0
Read/Write Bit
Figure 2-2. Register Description Key
2.2.1 Read/Write Bits
Read/write bits are typically control bits. They are, in general, not modified by a module. Reset indicates
the initial value of the latch.
2.2.2 Read-Only Bits
Read-only bits are status flag bits. They are indicators of module status. Reset indicates the value that
will be read immediately after system reset or before the module is enabled.
2.2.3 Write-Only Bits
Write-only bits are control bits. They typically return a state of 0 to prevent an inadvertent write to this bit
by a READ-MODIFY-WRITE instruction. Reset indicates the value that will be read immediately after
system reset, which is the forced read value (typically 0).
2.2.4 Reserved Bits
Reserved bits are read-only bits that typically read 0. Writes to these bits are ignored, and the user should
not write 1 for future compatibility. Reset indicates the value that will be read immediately after system
reset which is the forced read value (typically 0).
2.2.5 Reset Value
Values specified on the row marked Reset: are initial values of register bits after system reset. Those bits
unaffected by reset are marked with the letter U. Those bits that are unaffected by reset but initialized by
power-on reset are marked with an asterisk (*).
MC68HC05L16 • MC68HC705L16 Data Sheet, Rev. 4.1
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Freescale Semiconductor